1. Field of the Invention
The present invention is broadly concerned with vaccines for porcine reproductive and respiratory syndrome (PRRS). More particularly, the invention is concerned with the prevention of PRRS in swine by the administration of a vaccine comprising DNA subunits of PRRS virus (PRRSV). Still more particularly, the invention pertains to the use of open reading frame 1 (ORF1) in a DNA subunit vaccine which provides protective immunity against PRRSV to swine. Even more particularly, the invention pertains to the use of selected portions of ORF1 both alone and in combination with other portions of the PRRSV genome or in combination with other vaccines against PRRSV.
2. Description of the Prior Art
PRRS is a major disease in the swine industry worldwide. PRRS is caused by PRRSV infection. Currently, there are modified-live vaccines (MLV) available that, when used correctly, provide swine with protection against the clinical disease resulting from PRRSV infection. PRRS MLV vaccines require replication in the vaccinated animal in order to insure that an efficacious immune response is induced (for example, see Meng, X. J., Heterogeneity of Porcine Reproductive and Respiratory Syndrome Virus: Implications for Current Vaccine Efficacy and Future Vaccine Development; 74 Vet. Micro., 309-329 (2000)). However, such replication presents problems in that the PRRS MLV can persist in the animal for several weeks after vaccination and can also be shed to other PRRSV-negative swine. The shedding of PRRS MLV from vaccinated animals can be a problem in some swine herds that do not have good biosecurity measures in place to prevent shedding of PRRSV MLV from vaccinated animals to a PRRSV-naive population. Although millions of PRRS MLV doses have been used without issue, there are also sporadic reports in the literature as to the ability of the PRRS MLV to revert to a more virulent, wild-type strain of PRRSV. Attempts to solve the problems of PRRS MLV shed and possible reversion to virulence have also been tried by utilization of a vaccine comprised of inactivated PRRS virus (i.e. PRRS KV). However, research has shown that despite the fact that PRRS KV can induce a strong humoral response in vaccinated swine, it is not effective in preventing PRRS-associated disease.
Accordingly, what is needed in the art is a method of vaccination and vaccine that could induce the protective immune response, without the problems associated with PRRS MLV. Preferably, administration of the vaccine would not actively replicate in the vaccinated animal and would induce a strong humoral and cell-mediated immune response.